Added note to documentation about handling of whitespace

[dkondor]

Explicitly note that only space is allowed. Should clarify issue #703

[awulkiew]

Thanks for this PR @dkondor ! There are problems with it though.

Your comment is probably not going to be visible in the documentation. Have you built the docs and verified that it works as intended?

I think you have 4 options here:

1. Add it in the qbk file which is included below.
   https://github.com/boostorg/geometry/blob/develop/doc/reference/io/read_wkt.qbk
   It is included under Parameters section in the reference:
   https://www.boost.org/doc/libs/1_73_0/libs/geometry/doc/html/geometry/reference/io/wkt/read_wkt.html
   with the below

\qbk{[include reference/io/read_wkt.qbk]}

2. Add your comment in the \qbk{...} section which currently only includes the additional qbk file

\qbk{
Note that the wkt string ...

[include reference/io/read_wkt.qbk]
}

3. Add \details doxygen section and put the information there, like it is the case e.g. in area:
   https://github.com/boostorg/geometry/blob/develop/include/boost/geometry/algorithms/area.hpp#L300
   which is used to build this:
   https://www.boost.org/doc/libs/1_73_0/libs/geometry/doc/html/geometry/reference/algorithms/area/area_1.html
   Though in this case I'm not sure what to do with the link (see below). It is possible that enclosing it with \qbk{...} could work but I'm not sure. You should test it.

4. Add it in the documentation directory above
   https://github.com/boostorg/geometry/blob/develop/doc/reference/io/wkt_format.qbk
   which is used to build this page with general info:
   https://www.boost.org/doc/libs/1_73_0/libs/geometry/doc/html/geometry/reference/io/wkt.html

---

Furthermore we use QuickBook so the markup language is different than GitHub's. Links are defined as follows:

[@https://www.ogc.org/standards/sfa standard]

see QuickBook documentation.

---

Last but not least, I'm not sure where is the best place for this info. Without giving it much thought I'd say that either the \details section (3.) or the directory above with the general info about the standard (4.). What is your opinion @dkondor @mloskot @vissarion @barendgehrels?

[vissarion]

Last but not least, I'm not sure where is the best place for this info. Without giving it much thought I'd say that either the \details section (3.) or the directory above with the general info about the standard (4.). What is your opinion @dkondor @mloskot @vissarion @barendgehrels?

Adding this to the general info about the standard (4.) makes more sense to me.

[barendgehrels]

Replaced by #1106